2014-06-27 9:09 GMT+02:00 Thierry Reding <[email protected]>: > On Fri, Jun 27, 2014 at 08:58:21AM +0200, Johannes Pointner wrote: >> I know what you mean because I have here for example a panel that only >> supports a duty cycle between 20 and 100 percent. But wouldn't I be a >> possibility to add optional nodes with minimal/maximal brightness or >> something like that? > > We have something like that (lth_brightness) for non-DT and which was > supported in the first DT proposals. But again the equivalent using the > brightness-levels would be: > > brightness-levels = <0 20 21 ... 100>;
You are right this would be a possibility but I thought that configuring such ranges is much more readable than really writing it down. > > So the continuous range and low threshold are really just special cases > of what brightness-levels provides. Granted, it's somewhat tedious to > have to list ~100 values in a DT property like this, but I haven't > really heard any arguments why the range really needs to be that > fine-grained. Most of the devices that I've used have somewhere between > 8 and 20 brightness levels. An exception to this are Android devices, > which do indeed seem to support truly continuous ranges. In my case the fine granularity is demanded by our customers ( they are all used to desktop monitors where they can freely adjust the brightness even they don't really need that) and I have to make that somehow possible. But I understand your concerns. Hannes > > Thierry > >> >> Hannes >> >> >> 2014-06-27 8:12 GMT+02:00 Thierry Reding <[email protected]>: >> >> > On Fri, Jun 27, 2014 at 07:32:20AM +0200, Johannes Pointner wrote: >> > > Hello, >> > > >> > > I'm new working on the linux device drivers, so if I made something wrong >> > > please point me into the right direction. >> > > >> > > I'd like to use the pwm_bl driver for a sitara based terminal and for >> > this >> > > I would need the possibility to set the backlight within a percentage >> > > range. The following patch should add this possibility to the pwm_bl >> > > driver. The idea is to keep backward compatibility by moving the required >> > > option brightness levels to optional. Therefore if there is no node with >> > > brightness levels the percentage levels are used. >> > > >> > > Signed-off-by: Johannes Pointner <[email protected]> >> > > --- >> > > .../bindings/video/backlight/ >> > > pwm-backlight.txt | 11 +++--- >> > > drivers/video/backlight/pwm_bl.c | 46 >> > > ++++++++++++---------- >> > > 2 files changed, 31 insertions(+), 26 deletions(-) >> > >> > Also adding the backlight maintainers on Cc. >> > >> > This has been discussed a few times before. In fact the original device >> > tree binding had support for a continuous range of levels but that was >> > rejected during review. The reason was, as far as I remember, that the >> > number of levels and the corresponding duty cycle values is something >> > that's usually determined at system design time. Often backlights can't >> > properly light the whole surface of the panel at every level. >> > >> > That said, there's always the possibility to fake this by adding a DT >> > property with a continuous range, such as this: >> > >> > brightness-levels = <0 1 2 ... 100>; >> > >> > Thierry >> > -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
